Immunoglobulin G4-Related Lung Disease as an Incidental Finding After Surgical Resection of Lung Cancer

Pulmonary Adenosquamous Cell Carcinoma With Systemic Lymphadenopathy due to Immunoglobulin G4-Related Disease: A Case Report

A 75-year-old man with diabetes mellitus showed elevated C-reactive protein (CRP) level at his regular visit. Computed tomography scan showed a lung tumor in his left lower lobe and systemic lymphadenopathy including abdominal lymph nodes. The patient was diagnosed as primary pulmonary squamous cell carcinoma with systemic lymph node metastasis. Thereafter, unexpected steroid pulse therapy for accidental acute exacerbation of interstitial pneumonia rapidly shrank lymphadenopathy. At this time, we also found elevated serum immunoglobulin G4 (IgG4) level (385 mg/dL). Considering these findings, we doubted the lymph nodes metastases at the initial staging, and then corrected cancer-staging (C-staging) from inferior vena cava (IVC) to inferior abdomen (IA). In addition, during the steroid tapering, sudden onset and uncontrollable left pneumothorax required surgical approach. Curative-intent left lower lobectomy with lymphadenectomy was performed for the lung cancer. Pathological findings revealed coexistence of adenosquamous carcinoma and infiltration of IgG4-positive plasma cells in the resected mediastinal lymph node. We detected 384 IgG4-positive cells per high power field. IgG4/IgG-positive cell ratio was 54%. Based on these findings, the diagnosis of IgG4-related disease with primary adenosquamous carcinoma (p-stage IIIA) was confirmed. The patient died 24 days after surgery because of another acute exacerbation of interstitial pneumonia. Our case alerts oncologists to IgG4-related disease as a possible underlying comorbidity which may confuse pretreatment clinical stage.